This invention relates to a laser system including a nozzle for introducing a flow of shielding gas around an exiting laser beam. More particularly, this invention concerns such a nozzle having a means for backflowing a small amount of the incoming gas into a housing containing the laser mirror system.
Currently, lasers are being applied to manufacturing operations where they are used for thermal cutting and gouging as well as welding of metals. Lasers have been found to be especially useful in such applications and their use is increasing. Frequently it is desirable to shield the weld on a workpiece from the atmosphere by, e.g. providing a concentric column of shielding gas about the laser beam. This is accomplished most conveniently by utilizing a nozzle at the point where the focused laser beam exits from the housing of the laser system containing the reflecting mirrors.
A number of prior art systems are apparent which provide for the introduction of a gas through a manifold and into a laser nozzle and thence about a laser beam. Examples of these prior art attempts are shown in U.S. Pat. Nos. 3,569,660 to Holdcroft; 3,597,578 to Sullivan; and 3,696,230 to Friedrich. With these prior art systems, however, the shielding gas is prevented from moving backward into the laser system housing containing the focusing and concentrating mirrors by means of a window placed across the inlet to the nozzle. Additional sealing off of gas flow from the nozzle to the housing chamber is usually found in the form of an additional lens adjacent the mirror.
One problem engendered by having such a window is that, while initially clear, it tends to become obscured by contaminants during use. This results in a diminishing of the laser beam energy that can pass therethrough and subsequently through the nozzle and onto the workpiece. This, of course, results in a degradation in the output of the laser as seen by the workpiece. While some attempts have been made to direct the shielding gas onto the window to scour and clean it, this is not completely satisfactory, and the window must be periodically removed and replaced.
One way of avoiding this problem is to provide a laser system wherein the optical system includes a housing absent any window. One such system is shown in U.S. Pat. No. 3,907,408 to Engel, assigned to the Assignee hereof. With this type of system, there is full intercommunication between the interior of the laser optical system housing containing the mirrors and the interior of the nozzle. Without the window, the flow of shielding gas through the conventional laser nozzle and onto the workpiece causes an aspiration of gas to occur from the interior of the housing into the nozzle and thence onto the workpiece. If the housing is open to atmosphere, this results in an undesirable inclusion of atmospheric air with the shielding gas wherein it combines within the nozzle and is passed out onto the workpiece. This, of course, can result in poor-quality welds as the atmospheric air contacts the weld zone.